The present invention relates, generally, to four-stroke internal combustion engines and, more particularly, to four-stroke internal combustion engines used in trimmers, blowers, vacuums, chain saws, other hand-held power tools, snowblowers, generators, vegetation cutting devices such as lawn mowers, or other outdoor power equipment.
Many hand-held power tools or other outdoor power equipment are powered by electric motors or two-stroke internal combustion engines. Electric motors are limited to certain applications due to the available power for products utilizing a cord, and battery longevity for cordless products. Conventional two-stroke engines include a lubricating means in which the lubricant is mixed with fuel which allows the engines to operate in any given position such as upright, inclined, sideways or upside down. For example, when using a chain saw, the chain saw is typically capable of use in either an upright, sideways or upside down condition. Over the past few years, there has been a requirement by various governing bodies to reduce the emissions associated with all small gas engines, particularly, conventional two-stroke engines. Thus, because four-stroke engines do not require the mixing of lubricant and fuel, it is desirable to use four-stroke engines in place of conventional two-stroke engines, since four-stroke engines normally release fewer undesirable emissions as compared to the amount of undesirable emissions released by conventional two-stroke engines.
However, previously, it was widely viewed that four-stroke internal combustion engines could only be used for limited applications, such as lawn mowers, snowblowers, generators, or other portable products having wheels. It was thought that these prior four-stroke engines were too heavy and cumbersome to be used in operator-carried power tools. Moreover, since it is generally necessary to store oil separate from the gas so that the oil can be used for lubrication, traditional low-cost four-stroke engines were not designed to operate in any position other than a substantially upright position because if the engine was significantly tipped or tilted, the lubricant would foul the engine. Only very recently has it been contemplated that a four-stroke engine may be used in a hand-held power tool or in other applications where the engine may operate in a tipped or tilted condition.
Accordingly, there is a need for a four-stroke internal combustion engine that is capable of use in various power tools, and yet is also capable of having low emissions and being sufficiently light to be carried by an operator when desired. What is also needed is a four-stroke internal combustion engine that is capable of operating in many different attitudes of the engine. What is also needed is a four-stroke engine that eliminates the need for an elaborate lubrication system. What is needed is a four-stroke internal combustion engine which accomplishes these features and other features and which is also economical to manufacture.
In one embodiment of the present invention, there is provided a four-stroke internal combustion engine, preferably a side valve or xe2x80x9cLxe2x80x9d head engine, having an engine housing which includes a crankcase and a cylinder. A cylinder head which at least partially defines a combustion chamber is positioned adjacent to the cylinder. An intake valve and an exhaust valve are disposed within the engine housing. A crank chamber and an oil reservoir are disposed within the crankcase in such a way that the oil reservoir is in fluid flow communication with the crank chamber. A strategically placed agitator, located at least partially within the crank chamber, moves lubricant within the engine housing during operation of the engine to lubricate the necessary components of the engine.
A divider is disposed within the crankcase to at least partially divide the crank chamber and the oil reservoir. The divider assists in directing the lubricant during operation and storage of the engine in order to prevent a substantial amount of lubricant from undesirably migrating into the combustion chamber when the engine is operated or stored in an upright or tilted position. In one aspect of the present invention, the divider defines a path which extends about the divider. The path allows lubricant in the oil reservoir to flow around a substantial portion of the divider to further enhance the lubricating and storage features of the engine according to the principles of the present invention.
The engine is constructed of light weight material and appropriately sized so that the engine is sufficiently light enough to be usable in hand-held power tools. Thus, the four-stroke internal combustion engine according to the present invention may be utilized in those applications which are traditionally limited to the use of two-stroke internal combustion engines.
In one aspect of the present invention, the divider includes at least one opening such that the crank chamber and the oil reservoir are in fluid flow communication through the opening. The opening helps ensure that the crank chamber is substantially continuously lubricated during operation of the engine, even if the engine is operated under a tilted condition. The opening in the divider is positioned such that at least some of the lubricant found in the crank chamber after operation of the engine may flow back into the oil reservoir even if the engine is stored in a tilted state. Preferably, the divider includes a plurality of openings.
In another aspect of the present invention, the engine housing further includes a cylinder side wall which at least partially extends into the crank chamber to define a lubricant receiving space between the divider and the cylinder side wall. Preferably, the cylinder side wall at least partially defines a piston bore. During operation, as the agitator mixes and slings lubricant around the inside cavity of the engine as a result of the rotating action of the agitator, the lubricant is more likely to be slung into the open area between the divider and the cylinder side wall rather than into the piston bore. Moreover, during storage, the open area or lubricant receiving space provides additional space for the lubricant to be held if the engine is stored in a sideways or upside down position to also prevent a substantial amount of the lubricant from flowing into the piston bore. As previously noted, migration of the lubricant into the combustion chamber leads to an unwanted condition. A function of the lubricant receiving space is to inhibit lubricant from reaching the piston bore, thereby preventing a substantial amount of lubricant from reaching the combustion chamber.
In another aspect of the present invention, the engine housing further includes a valve chamber. The intake valve and exhaust valve are disposed within the valve chamber and the valve chamber is in fluid flow communication with the crank chamber. The operation of the agitator, the pressure pulses created within the engine during operation of the engine, the communication of the oil reservoir with the crank chamber, and the communication of the crank chamber with the valve chamber together allow the working components found within the valve chamber to be lubricated, even if the engine is operated in a tilted manner. Preferably, the valve chamber is also in fluid flow communication with the cylinder side wall to further enhance the lubrication of the working components located within the valve chamber. The strategic positioning of the fluid flow openings into the valve chamber will prevent the valve chamber from receiving too large of a quantity of lubricant when the engine is being operated or being stored.
In another embodiment of the present invention, the engine includes a cantilevered crankshaft which has opposite ends and which is substantially located within the crank chamber. The agitator includes a counterweight which is interconnected to the cantilevered end of the crankshaft. The counterweight is adapted to reduce windage resistance on the crankshaft and to sling lubricant about the crank chamber as the crankshaft rotates during operation of the engine. Further, the counterweight throws the lubricant away from the main bearings of the crankshaft, thereby substantially preventing the main bearings from being flooded by the lubricant during operation of the engine. The divider may be provided with a scraper which is used to limit the amount of lubricant which comes into contact with the agitator or the counterweight. The scraper preferably at least partially extends into the crank chamber, so that as the agitator rotates past the scraper during operation of the engine, the scraper meters the amount of lubricant which comes into contact with the agitator.
In another aspect of the present invention, a cam shaft disposed substantially normal to the crankshaft is rotatably driven by the crankshaft. The substantially normal arrangement of the cam shaft and crankshaft enables the engine to be longer in a direction parallel to a power take off, as compared to a conventional engine in which the cam shaft is parallel with the crankshaft. Such an engine is desirable in certain hand-held power tool applications, such as power trimmers, in order to provide an overall better balance of the power tool for the convenience of the user. The substantially normal arrangement of the shafts also allows for an intake port and an exhaust port disposed in the cylinder to be significantly spaced apart. Segregating the ports will reduce heat migration from the exhaust port to the intake port which could result in hot restart (e.g., vapor lock) problems.
Preferably, the intake and exhaust ports are elliptical in shape. The elliptical configuration of the ports enables the overall profile or height of the engine housing to be reduced, thereby reducing the amount of material needed for the overall engine housing. This helps reduce the overall weight of the engine housing. The port walls are provided with sufficient surface area and strength to support the portion of the engine housing and cylinder head disposed above the ports. The substantially normal relationship between the crankshaft and the cam shaft also allows the valves to be disposed substantially normal to the crankshaft. A first valve tappet associated with the intake valve and a second valve tappet associated with the exhaust valve operatively engage the cam shaft to provide for the proper operation of the valves with respect to a four-stroke internal combustion engine. Such a compact arrangement further limits the overall weight of the engine.
In another embodiment of the present invention, a breather arrangement for the four-stroke internal combustion engine is provided. The cam shaft is provided with an axial passageway and several radial apertures. The radial apertures communicate with the crank chamber and the passageway. A breather tube communicates with the passageway and an air intake system of the engine. A check-valve is positioned between the end of the cam shaft and the air intake system to maintain the negative pressure created within the engine. Blow-by gas inside the engine is admitted into the radial aperture of the cam shaft and is sent through the axial passageway of the cam shaft and into the breather tube, so that the blow-by gas is recirculated within the engine. The pressure pulses created within the engine cause the blow-by gas to enter the cam shaft and be recirculated as described. However, the centrifugal action of the cam shaft counters the action created by the pressure pulses, thereby substantially preventing the heavier lubricant, as compared to the blow-by gas, from entering the radial apertures in the cam shaft. As a result, the lubricant will substantially remain within the cavity of the engine and will not travel through the breather tube to the air intake system of the engine.
In another aspect of the present invention, the engine housing is designed to cooperate with a piston found within the piston bore such that a connecting rod can be conveniently attached to the piston and the crankshaft. The crankcase and the piston each include an access hole. A connecting rod is operatively attached to the crankshaft and the piston in the following manner. The access hole in the crankcase and the access hole or aperture in the piston are aligned during installation of a wrist pin. The wrist pin is inserted into the piston aperture and through an end of the connecting rod to connect the connecting rod to the piston. A star washer is used to hold the wrist pin in place after instillation.
The compact size of the engine according to the present invention and the cantilevered crankshaft make it difficult to assemble the internal components of the engine, such as the piston-connecting rod-crankshaft assembly. The cooperation of the access holes in the crankcase and the piston allow for easy assembly of the piston-connecting rod-crankshaft assembly. Preferably, it is desirable to use the same engine housing casting for engines having different horsepower ratings, simply by changing the connecting rod and thus, the length of the piston throw. To facilitate assembly and to permit the same engine housing casting to be used for different sized engines, an elliptical, or the like, wrist pin boss is formed in the crankcase of the engine housing. The wrist pin boss can be machined at its upper end to provide an access hole in the crankcase for a first horsepower rating or piston throw, and the wrist pin boss can be machined at its lower end to provide an access hole in the crankcase for a second horsepower rating or piston throw. After the wrist pin boss is properly machined, the wrist pinxe2x80x94which connects the piston to the connecting rodxe2x80x94is inserted through the crankcase aperture and into the piston aperture as previously explained. In this way, the same engine housing casting can be used for different sized engines.
In another aspect of the present invention, the crank chamber includes at least two bearing pockets. One of the pockets has a larger diameter than the other. Both of the bearing pockets are disposed on the same side of the internal cylinder side wall. The cantilevered crankshaft is supported by two main bearings located in the respective bearing pockets. The bearing pocket nearest the cantilevered (input) end of the crankshaft is the larger diameter bearing pocket so that the bearing pockets can be machined in the crank chamber from the same side with a single tool thereby eliminating unnecessary tooling requirements. This provides a significant savings in capital costs and manufacturing expenses. Preferably, before assembling the crankshaft in the crank chamber, the outer bearing and then the agitator or counterweight are properly positioned around the cantilevered end of the crankshaft. The counterweight is provided with an access aperture in order to allow a tool to appropriately contact the adjacent bearing and the crankshaft. In this way, as the crankshaft is placed into the crank chamber, the bearing is not damaged and the crankshaft is properly positioned.
In another aspect of the present invention, the combustion chamber is adapted to enhance swirl of the air/fuel mixture to increase efficiency of the engine. Preferably, a spark plug is positioned closer to the exhaust valve than the intake valve to also improve engine efficiency, and reduce the likelihood of self-ignition within the engine.
In another aspect of the present invention, the engine housing is designed in such a way so as to permit two engine housings to be produced using only one die tool and one die casting machine. This also reduces capital costs and manufacturing expenses.
In another aspect of the present invention, a starter assembly is attached to the rear of the engine and is designed to utilize a crankshaft pin which is integral with the crankshaft. The crankshaft pin is the contact point for the internal rotation of the crankshaft in order to start the engine.
In another aspect of the present invention, the blower housing has an inwardly extending hub. The hub fits over the crankshaft. The starter assembly slides onto the hub. A star washer or the like is placed over the hub so as to prevent the axial movement of the starter assembly, particularly the pulley. This arrangement eliminates the need for separate mounting bosses and fasteners which are normally needed to attach the starter assembly to the blower housing and which typically block the cooling air flow by the fan.
In another aspect of the present invention, a shroud is provided to at least partially surround the engine housing. The shroud is provided with a pair of opposed channels. A fuel tank having opposed, outwardly extending shoulders is held by the shroud as the shoulders are received by the respective channels. Preferably, a filler material is positioned between each of the channels and respective shoulders so as to provide a more snug fit between the shroud and the fuel tank.
In a preferred embodiment, a fuel line includes a fuel filter attached to the end of the fuel line disposed within the fuel tank. The fuel filter acts as a weight. During operation of the engine, as the engine is tipped in different orientations, the weighted fuel line swings to the bottom of the fuel tank so that fuel is always picked up by the fuel line regardless of the orientation of the engine.
In one aspect of the present invention, the shroud includes an opening around the intake port. An intake isolator is provided having an air/fuel passageway extending therethrough. The intake isolator is mounted to the engine housing so that the air/fuel passageway of the intake isolator is aligned with the intake port. Further, the intake isolator is positioned within the opening of the shroud to substantially ensure that cooling air passing between the engine housing and the shroud cannot escape through the opening in the shroud. The intake isolator is also used to insulate the intake air/fuel mixture from the surrounding environment to the extent feasible to ensure that the air/fuel ratio remains substantially correctly calibrated. In one embodiment of the present invention, a carburetor is interconnected with the intake isolator.
In one aspect of the present invention, the shroud includes a plurality of raised portions on one side thereof. If desired, the engine can be placed on the ground to rest on the raised portions. This could be useful, for example, on a trimmer when the user desires to change the cutting line located on the end of the shaft which is spaced a significant distance from the engine.
In another aspect of the present invention, the engine housing includes a back plate which is adjacent to a flywheel. Preferably, the crankcase, the cylinder and the back plate are cast as a single component, thereby reducing manufacturing and assembly costs, and thereby limiting the overall size of the engine housing. In a preferred embodiment, the engine housing further includes at least one fin integrally formed thereto. The fin extends from the back plate and beneath the crankcase to increase the stability between the back plate and the crankcase. The fin also is adapted to help cool the engine housing, particularly, the crankcase.
In another aspect of the present invention, a muffler is connected to the engine housing. The muffler includes a boss which extends into the exhaust port. In one embodiment, the engine housing includes an angled, stepped sealing surface located in the exhaust port. The end of the muffler boss mates against the exhaust port sealing surface to substantially prevent the exhaust from undesirably escaping into the surrounding atmosphere. Preferably, a sealing gasket is positioned between the end of the boss and the exhaust port sealing surface to even better prevent the exhaust from undesirably escaping into the atmosphere. In another embodiment, the muffler boss is surrounded by a portion of the exhaust port to define a clearance between the outside liner of the boss and the adjacent surface of the exhaust port. A gasket is positioned between the muffler and the engine housing to seal the clearance space between the muffler and the engine housing so as to prevent exhaust from undesirably escaping into the atmosphere. In a preferred embodiment, the gasket is an enlarged gasket which also serves as a heat shield between the engine housing and the user.
In one aspect of the present invention, the muffler includes a pair of outer shells having a pair of mounting bolt holes extending therethrough for receiving a pair of mounting bolts. A pair of bolt receiving bores are located on opposite sides of the exhaust port in the engine housing. This arrangement ensures that the muffler will be securely attached to the engine housing in a stable manner. In a preferred embodiment, the muffler includes an inner shell sandwiched between the outer shells. The inner shell is a baffle plate adapted to reduce the amount of exhaust admitted into the atmosphere. The inner shell also includes a pair of mounting bolt holes to receive the mounting bolts. In yet another preferred embodiment, one of the outer shells includes a shoulder extending around an edge of the outer shell. The other outer shell includes a hook-shaped flange extending around an edge of the outer shell. The hook-shaped flange of the one outer shell receives the shoulder of the other outer shell upon assembly of the muffler. The assembly is such that if exhaust leaks out of the muffler, the exhaust will leak away from the engine housing so as not to substantially heat the engine housing.
In one aspect of the present invention, the four-stroke internal combustion engine includes an engine housing having an integrally formed crankcase, cylinder and flywheel back plate. The flywheel back plate includes at least one mounting boss on one side and at least one other mounting boss on an opposite side. An assembly fixture is utilized to hold the engine housing during assembly of the engine. Each mounting boss on the flywheel back plate receives a separate pin of the assembly fixture to secure the engine housing to the assembly fixture. A shroud is provided to at least partially surround the engine housing. The shroud includes at least two slots such that the slots surround the pins of the assembly fixture when the shroud is positioned around the engine. The shroud can then be firmly attached to the engine. After the shroud is attached to the engine, the pins can be removed from the mounting bosses. In this manner, the engine can be substantially completely assembled while the engine is mounted to the assembly fixture.
Accordingly, it is a principal feature of the present invention to provide a four-stroke internal combustion engine which includes a simple and inexpensive lubricating system which enables the engine to be functional in various operational attitudes.
It is a feature of the present invention to provide a four-stroke engine incorporating the foregoing features and yet also simple and easy to manufacture and assemble.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings.